Some functional surface modifying endgroups (SMEs), such as hydrocarbons, fluorocarbons, silicones, linear PEOs and sulfonates, have been demonstrated in biomedical polymers to improve biocompatibility and biostability. These biomedical polymers may, for example, be used as a casing to enclose an implantable biomedical device (IMD). A small concentration of the surface modifying endgroups, which terminates the ends of a base polymer, modifies the surface properties of the base polymer without significantly modifying bulk properties. Low bulk concentrations of the SME can produce essentially complete monolayer coverage.
The surface modifying endgroups (SMEs) migrate to the surface of the polymer. Thus, if the polymer is used as a casing for an implantable medical device, the end groups will migrate to the surface of the IMD. This surface develops spontaneously by surface-energy-reducing migrations of the SME to the air-facing surface. Interfacial energy continues to form the surface in response to a change in environment, e.g., following implantation into a patient and tissue contact. Surface modification is thought to reduce protein adsorption and platelet adhesion, possibly minimizing tissue encapsulation. However, current SMEs cannot provide a sufficiently think cover on the base polymer surfaces because linear molecules are used for the SMEs. It is believed that polymers having low SME coverage may be ineffective in improving long-term biocompatibility and biostability in implantable biomedical devices.